Sweet Potato Weevil

Cylas formicarius

The Sweet potato Weevil is a native of tropical areas, but has been established in the USA since at least 1875. This insect is the biggest sweet potato pest in most areas as it not only causes damage in the field, but also in storage. It can complete a life cycle in little over a month and can produce many generations in a warm summer. The adult looks somewhat like a reddish ant with a long curved snout, the larvae is a small white grub, with a darker head. The female lays eggs one at a time at the base of the stem and when it hatches the larvae tunnels down into the tuber. It continues to eat tunnels in the tuber until it matures, when the adult eventually emerges from a hole in the tuber (though it may stay inside the tuber feeding for a while). In extreme cases damage can be severe (it may cause so much root damage the leaves turn yellow), in others it may be a minor problem. Of course the tunneled tubers aren’t really edible.

This weevil overwinters as an adult and needs food to survive, so you can control it by making sure it has nothing to eat. Do this by good sanitation, removing all roots and crop debris from the soil, along with any wild morning glories (Ipomoea species) growing nearby. Also be sure to rotate crops for at least 3 years, Parasitic nematodes can also be used as a control.

Image: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org